1. Field of the Invention
This invention relates to a method of recovering polyhydroxyalkanoates (PHAs), and more particularly to a method of recovering PHAs from municipal waste sludge.
2. Description of the Related Art
Polyhydroxyalkanoates (PHAs) are capable of being synthesized by microbial species present in municipal waste sludge or in an environment containing a carbon source and limited nutrients, such as nitrogen, phosphorous, sulfur, oxygen, magnesium, etc. PHAs are aliphatic polyesters accumulated in cells of PHAs producing microbial species. Polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV) are commonly known PHAs that are synthesized by microbial species. PHAs are biodegradable, extendable and thermoplastic materials that are similar to polyethylene (PE) and polystyrene (PS) in terms of physical properties.
With environmental problems becoming more serious, the recovery of PHAs has attracted more interest. In conventional methods, microbial species are cultured to produce PHAs, which are then recovered by extraction. Examples of the conventional methods are disclosed in U.S. Pat. No. 7,141,400, Taiwan patent no. 283250, WO publication no. 2006/035889 and US patent application publication no. 2008/0193987.
PHAs are recovered using sodium hypochlorite, chloroform, or a surfactant in the prior art disclosed in (1) E. Berger et al., “PHB recovery by hypochlorite digestion of non-PHB biomass,” Biotechnology Techniques (1989), vol. 3, no. 4, pages 227-232; (2) Sei Kwang Hahn et al., “Optimization of microbial poly(3-hydroxybutyate) recovery using dispersions of sodium-hypochlorite solution and chloroform,” Biotechnology and Bioengineering (1994), vol. 44, pages 256-261; (3) J. A. Ramsay et al., “Recovery of poly-3-hydroxyalkanoic acid granules by surfactant-hypochlorite treatment,” Biotechnology Techniques (1990), vol. 4, no. 4, pages 221-226; (4) Shih-Chen Tang, “Producing different polyhydroxyalkanates by microorganisms,” Masters Thesis, 2007, Yuan Ze University, Department of biotechnology and bioinformatics; and (5) Xuping X U, et al., “Study on poly-hydroxybutyrate (PHB) extraction from sphaerotilus natans by sodium hypochlorite-chloroform,” Journal of FUJIAN normal university (natural science edition) (2004) vol. 20, no. 1, pages 74-77.
However, in order to obtain PHAs in relatively high purity and yield using the conventional methods, suitable microbial cells should be selected, and proper nutrients are needed to culture the microbial species with a sufficient period of time. Accordingly, the cost for recovery of PHAs using the conventional methods is high.